Anyone who has ever suffered a sunburn knows that too much exposure to UV radiation is bad for your skin. But in the moment, it can be hard to tell when you’ve gotten too much sun—especially during the winter, when you might not think you need sunscreen. (In reality, snow reflects up to 80 percent of the sun’s UV light, so you may end up getting hit with the same rays twice.) A new wearable sensor spotted by Wired aims to make understanding your sun exposure a whole lot easier.

L'Oréal’s new La Roche-Posay My Skin Track UV sensor pairs with a smartphone app to alert users when they’ve had high levels of UV exposure. Developed by L'Oréal’s Tech Incubator in collaboration with Northwestern University engineering professor John Rogers and Swiss designer Yves Béhar, the sensor measures UVA rays (which are associated with skin aging and skin cancer) and uses an algorithm to calculate UVB exposure (which is associated with sunburn and skin cancer).

The UV sensor
L'Oréal USA

At only half an inch tall and 1.3 inches long, the waterproof sensor is designed to be discreetly attached to your clothes, watchband, or sunglasses. The sensor's LED detector measures UV rays as sunlight passes through a small window in the device, then transfers the data to your phone via a near-field communication (the same technology in some hotel key cards). It stores the photons from the UV rays in a capacitor, eliminating the need for a battery.

Based on this data, the My Skin Track app can tell you how close you're getting to the maximum limit of UV exposure doctors recommend per day. It also provides updates about the air quality, pollen count, and humidity wherever you are at any given moment. Based on this information, as well as data about your specific skin type and skin tone, the app's Skin Advice feature will provide customized tips for keeping your skin healthy. It also recommends specific products—La Roche-Posay items can be bought directly through the app, should you desire.

The sensors are exclusively available through Apple stores. You can order one online for $59.95.

[h/t Wired]